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Class 9, Science, Chapter-2, Lecture-1, Mixture (Notes)

ELEMENT:

The simplest form of matter which cannot be decomposed, by ordinary chemical means, into simpler substances, nor can be formed by combination of other substances is called element.

Classification:

  1. Metals: Solid (Mercury is the only Liquid metal)
    Hard (Exception-Sodium, Potassium)
    Good conductors.
  2. Non-Metals: Gaseous or Solid (Bromine is the only Liquid non-metal)
    Soft (Exception-Diamond)
    Bad conductor (Exception-Graphite)

COMPOUND:

A pure substance formed from two or more elements combined together in definite proportion by weight is called a compound.

Properties of Compounds:

  1. The constituent elements cannot be separated by physical methods.
  2. The properties of compounds are different from those of its constituents.
  3. The constituent elements are present in a fixed proportion by weight.
  4. Compounds have a fixed melting and boiling point.
  5. A compound is a homogeneous substance.
  6. A compound has a definite formula.
  7. Energy is released or absorbed during formation of compounds.

MIXTURE:

A substance containing two or more elements or compounds in any proportion and the components of which can be separated by simple mechanical methods is called a mixture.
Examples: Air, Gun powder, Steel.

Types of Mixture (On the basis of composition):

  1. Homogeneous Mixture:
    A mixture which has a uniform composition throughout its mass is called homogeneous mixture.
  2. Heterogeneous Mixture:
    A mixture which does not have a uniform composition throughout its mass is called heterogeneous mixture.

Properties of Mixture:

  1. The constituents can be separated by physical methods like filtration, evaporation, sublimation, magnetic separation.
  2. It retains the properties of its constituents.
  3. The constituents may be present in any ratio.
  4. Mixtures do not have fixed melting point or boiling point.
  5. Mixtures may be homogeneous or heterogeneous.
  6. Mixtures do not have definite formulae.
  7. Energy is neither given out nor absorbed during formation of mixtures.

Differences Between:

Mixture

Compound

No new substance is formed.

New substance is formed.

Composition of mixture is variable.

Composition of compound always remains same.

Constituents retain their properties.

Constituents lose their properties.

Constituents can be separated by physical methods.

Constituents cannot be separated by physical methods.

Differences Between:

Element

Compound

Cannot be split up into two or more different substances.

Can be split up into two or more different substances

Made up of atoms of same kind

Made up of atoms of different kinds.

Made up of the same substance

Made up of two or more different substances